The present invention is directed to cooling assemblies and other apparatus used for removing heat from electronic devices. More particularly, it relates to a closed-cycle coolant impingement assembly integrated with an electronic module, and to a control method therefore.
As is well known, as the circuit density of electronic chip devices increases, there is a correspondingly increasing demand for the removal of heat generated by these devices. The increased heat demand arises both because the circuit devices are packed more closely together and because the circuits themselves are operated at increasingly higher clock frequencies. Nonetheless, it is also known that runaway thermal conditions and excessive heat generated by chips is a leading cause for failure of chip devices. Furthermore, it is anticipated that the demand for heat removal from these devices will increase indefinitely. Accordingly, it is seen that there is a large and significant need to provide useful cooling mechanisms for electronic devices.
Limitations of bulk complementary metal oxide semiconductor (CMOS) scaling will soon be reached, and other means to enhance circuit performance are being investigated. One approach is to operate circuits at low temperatures. Towards this end, a refrigeration system is proposed herein to cool, for example, the processor module or other heat generating components of a computer system. The heat produced by CMOS chips is conventionally conducted through a compliant paste gap, across an encapsulation hat, and into an evaporator of a refrigeration system. The desire to cool higher and higher powered multichip modules to lower and lower temperatures places the use of a paste encapsulated module in question. The ability of the paste to provide its function at very low temperatures is suspect, and the higher heat fluxes tend to drive more complex and costly evaporator designs. An alternate approach to cooling an electronic module is thus desirable.
Briefly summarized, in one aspect the present invention comprises an electronic module and integrated refrigerant evaporator assembly which includes a plurality of heat generating electronic components arrayed on a substrate. The evaporator assembly is disposed over the electronic components such that the electronic components reside in a chamber between the substrate and the refrigerant evaporator assembly. The refrigerant evaporator assembly is configured to direct coolant onto the plurality of heat generating electronic components, which may comprise integrated circuit chips. More particularly, the evaporator assembly includes a lower plate which has a plurality of jet orifices that are arrayed to direct coolant onto the plurality of heat generating electronic components. The lower plate further includes a plurality of channels formed between at least some of the plurality of jet orifices. The plurality of channels are designed to remove coolant from the chamber after the coolant is heated by the plurality of heat generating electronic components.
In another aspect, a closed-cycle cooling system for an electronic module is provided. The closed-cycle cooling system includes a coolant delivery and extraction system having a delivery branch and an extraction branch. A first control valve is located in the delivery branch and a second control valve is located in the extraction branch. The electronic module includes at least one heat generating electronic component disposed on a substrate, and a refrigerant evaporator assembly disposed over the at least one heat generating electronic component. The at least one heat generating electronic component resides in a chamber defined between the substrate and the evaporator assembly. The evaporator assembly is configured to direct coolant onto the at least one heat generating electronic component when in use, and has an inlet coupled to the delivery branch and an outlet coupled to the extraction branch. The closed-cycle cooling system further includes a controller for controlling the first control valve and the second control valve to limit pressure within the chamber when initiating and when discontinuing flow of coolant within the closed-cycle cooling system.
In a further aspect, control methods are provided for controlling coolant flow within the closed-cycle cooling system in order to protect the electronic module and integrated refrigerant evaporator assembly from experiencing high coolant pressure at startup and shutdown of the closed-cycle cooling system. Startup is controlled by turning the system""s compressor on, and thereafter opening a control valve in the extraction branch of the closed-cycle cooling system, and subsequently opening a control valve in the delivery branch of the closed system. Pressure is controlled at shutdown by first closing the control valve in the delivery branch, waiting until coolant pressure within the assembly is less than a predetermined setpoint, then closing the control valve in the extraction branch, and thereafter turning the compressor off.
To restate, provided herein is an electronic module having an integrated jet impingement refrigerant evaporator assembly, as well as a control method therefor. Advantageously, the electronic module with integrated evaporator proposed herein is compact and has a low profile. Furthermore, since heat transfer takes place directly between a refrigerant and the semiconductor chips of the module, the evaporator can be made of lightweight, low thermal conductivity materials such as hard plastics. Materials of this type have low thermal capacitance which minimizes initial cool-down time, plus the low thermal conductivity helps to reduce parasitic heat load inherent in low temperature systems. In addition, since tolerances (with the exception of the jet orifices) are not as critical as those of today""s module hardware, the cost of producing the evaporator should be relatively low. Subsections may even be molded or pressed (e.g., stamped) with minimal finishing or machining required.
Furthermore, the pressure drop across the jet orifice hat can easily be higher than conventional pump flow systems can practically provide. For example, typical centrifugal pumping systems will not tolerate much more than a 10 psi orifice pressure drop. This limits jet velocity and thus heat transfer capability. In a refrigeration system, pressure drops across expansion devices are typically more than 150 psi. This pressure drop can now be proportioned between the expansion device and the jet orifices to optimize heat transfer and still attain low refrigerant temperatures.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered part of the claimed invention.